Cotton variety 18R421B3XF

ABSTRACT

The invention relates to the novel cotton variety designated 18R421B3XF. Provided by the invention are the seeds, plants, plant parts and derivatives of the cotton variety 18R421B3XF. Also provided by the invention are methods of using cotton variety 18R421B3XF and products derived therefrom. Still further provided by the invention are methods for producing cotton plants by crossing the cotton variety 18R421B3XF with itself or another cotton variety and plants and seeds produced by such methods.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates generally to the field of cotton breeding.In particular, the invention relates to the novel cotton variety18R421B3XF.

Description of Related Art

The goal of a commercial cotton breeding program is to develop new,unique and superior cotton varieties. In cotton, important traitsinclude, but are not limited to, higher fiber (lint) yield, earliermaturity, improved fiber quality, resistance to diseases and insects,tolerance to drought and heat, and improved agronomic traits. Thebreeder selects and crosses two or more lines, followed by generationadvancement and selection, thus producing many new genetic combinations.The breeder can theoretically generate billions of different geneticcombinations via this procedure.

SUMMARY OF THE INVENTION

One aspect of the present invention relates to seed of the cottonvariety 18R421B3XF. The invention also relates to plants produced bygrowing the seed of the cotton variety 18R421B3XF as well as thederivatives of such plants. As used herein, the term “plant” includesplant cells, plant protoplasts, plant cells of a tissue culture fromwhich cotton plants can be regenerated, plant calli, plant clumps, andplant cells that are intact in plants or parts of plants, such aspollen, flowers, seeds, bolls, leaves, stems, and the like.

Another aspect of the invention relates to a tissue culture ofregenerable cells of the cotton variety 18R421B3XF as well as plantsregenerated therefrom, wherein the regenerated cotton plant is capableof expressing all of the morphological and physiological characteristicsof a plant grown from the cotton seed designated 18R421B3XF.

Yet another aspect of the current invention is a cotton plant of thecotton variety 18R421B3XF further comprising a single locus conversion.In one embodiment, the cotton plant is defined as comprising the singlelocus conversion and otherwise capable of expressing all of themorphological and physiological characteristics of the cotton variety18R421B3XF. In particular embodiments of the invention, the single locusconversion may comprise a transgenic gene which has been introduced bygenetic transformation into the cotton variety 18R421B3XF or aprogenitor thereof. A transgenic or non-transgenic single locusconversion can also be introduced by backcrossing, as is well known inthe art. In certain embodiments of the invention, the single locusconversion may comprise a dominant or recessive allele. The locusconversion may confer potentially any trait upon the plant as describedherein. In specific embodiments of the invention, a locus conversion mayconfer one or more traits such as, for example, male sterility,herbicide tolerance, insect resistance, disease resistance, waxy starch,modified fatty acid metabolism, modified phytic acid metabolism,modified carbohydrate metabolism and modified protein metabolism. Incertain embodiments, a potential locus conversion that confers herbicideresistance may confer resistance to herbicides such as, for example,imidazolinone herbicides, sulfonylurea herbicides, triazine herbicides,phenoxy herbicides, cyclohexanedione herbicides, benzonitrileherbicides, 4-hydroxyphenylpyruvate dioxygenase-inhibiting herbicides,protoporphyrinogen oxidase-inhibiting herbicides, acetolactatesynthase-inhibiting herbicides, 1-aminocyclopropane-1-carboxylic acidsynthase-inhibiting herbicides, bromoxynil, nicosulfuron,2,4-dichlorophenoxyacetic acid (2,4-D), dicamba, quizalofop-p-ethyl,glyphosate, or glufosinate.

In another aspect of the invention, a plant of cotton variety 18R421B3XFis provided further comprising a transgene. The transgene may comprise anaturally occurring cotton gene or recombinant DNA. In certainembodiments of the invention, the transgene confers traits such as, forexample, male sterility, waxy starch, herbicide resistance, insectresistance, resistance to bacterial, fungal, nematode or viral disease,and altered fatty acid, phytate, or carbohydrate metabolism.

Still yet another aspect of the invention relates to a method ofgenerating a plant of cotton variety 18R421B3XF with a modified genomeby introducing a transgene or single locus conversion. A transgenic ornon-transgenic single locus conversion can be introduced bybackcrossing, as is well known in the art. The transgene may beintroduced through genetic transformation techniques, as are also wellknown in the art.

Still yet another aspect of the invention relates to a first generation(F₁) hybrid cotton seed produced by crossing a plant of the cottonvariety 18R421B3XF to a second cotton plant. Also included in theinvention are the F₁ hybrid cotton plants grown from the hybrid seedproduced by crossing the cotton variety 18R421B3XF to a second cottonplant. Still further included in the invention are the seeds produced byF₁ hybrid plants, which have a plant of the cotton variety 18R421B3XF asone parent; the second generation (F₂) hybrid cotton plants grown fromthe seeds produced by those F₁ hybrid plants; and the seeds produced bythose F₂ hybrid plants.

In a further aspect of the invention, a composition is providedcomprising a seed of cotton variety 18R421B3XF comprised in plant seedgrowth media. In certain embodiments, the plant seed growth media is asoil or synthetic cultivation media. In specific embodiments, the growthmedia may be comprised in a container or may, for example, be soil in afield. Plant seed growth media are well known to those of skill in theart and include, but are in no way limited to, soil or syntheticcultivation media. Plant seed growth media can provide physical supportfor seeds and can retain moisture and/or nutritional components.Examples of characteristics for soils in certain embodiments can befound, for instance, in U.S. Pat. Nos. 3,932,166 and 4,707,176.Synthetic plant cultivation media are also well known in the art andmay, in certain embodiments, comprise polymers or hydrogels. Examples ofsuch compositions are described, for example, in U.S. Pat. No.4,241,537.

Still yet another aspect of the invention is a method of producingcotton seeds comprising crossing a plant of the cotton variety18R421B3XF to any second cotton plant, including itself or another plantof the variety 18R421B3XF. In particular embodiments of the invention,the method of crossing comprises: (a) planting seeds of the cottonvariety 18R421B3XF; (b) cultivating cotton plants resulting from saidseeds until said plants bear flowers; (c) allowing fertilization of theflowers of said plants; and (d) harvesting seeds produced from saidplants.

Still yet another aspect of the invention is a method of producinghybrid cotton seeds comprising crossing the cotton variety 18R421B3XF toa second, distinct cotton plant which can be nonisogenic to the cottonvariety 18R421B3XF. In particular embodiments of the invention, thecrossing comprises: (a) planting seeds of cotton variety 18R421B3XF anda second, distinct cotton plant; (b) cultivating the cotton plants grownfrom the seeds until the plants bear flowers; (c) cross-pollinating aflower on one of the two plants with the pollen of the other plant; and(d) harvesting the seeds resulting from the cross-pollinating.

Still yet another aspect of the invention is a method for developing acotton plant in a cotton breeding program comprising: (a) obtaining acotton plant, or its parts, of the variety 18R421B3XF; and (b) employingsaid plant or parts as a source of breeding material using plantbreeding techniques. In the method, the plant breeding techniquesinclude, but are not limited to, recurrent selection, mass selection,bulk selection, backcrossing, pedigree breeding, genetic marker-assistedselection and genetic transformation. In certain embodiments of theinvention, the cotton plant of variety 18R421B3XF is used as the male orfemale parent.

Still yet another aspect of the invention is a method of producing acotton plant derived from the cotton variety 18R421B3XF, the methodcomprising the steps of: (a) preparing a progeny plant derived fromcotton variety 18R421B3XF by crossing a plant of the cotton variety18R421B3XF with a second cotton plant; and (b) crossing the progenyplant with itself or a second plant to produce a progeny plant of asubsequent generation which is derived from a plant of the cottonvariety 18R421B3XF. In one embodiment of the invention, the methodfurther comprises: (c) crossing the progeny plant of a subsequentgeneration with itself or a second plant; and (d) repeating steps (b)and (c) for at least 2-10 additional generations to produce an inbredcotton plant derived from the cotton variety 18R421B3XF. Also providedby the invention is a plant produced by this and the other methods ofthe invention. Plant variety 18R421B3XF-derived plants produced by thisand the other methods of the invention described herein may, in certainembodiments of the invention, be further defined as comprising thetraits of plant variety 18R421B3XF given in Table 1.

The use of the word “a” or “an” when used in conjunction with the term“comprising” in the claims and/or the specification may mean “one,” butit is also consistent with the meaning of “one or more,” “at least one,”and “one or more than one.”

Other objects, features and advantages of the present invention willbecome apparent from the following detailed description. It should beunderstood, however, that the detailed description and the specificexamples, while indicating specific embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides, in one aspect, methods and composition relatingto plants, seeds and derivatives of the cotton variety 18R421B3XF.Cotton variety 18R421B3XF was developed from an initial cross of[A1088572]*5/[08Y619B2R2-DGT-B3R2-T1G5]. The breeding history of thevariety can be summarized as follows:

Gener- ation Year Description Cross 2013 Cross was made in Juana Diaz,PR between donor parent 08Y619B2R2-DGT-B3R2-T1G5 and recurrent parentA1088572. F₁ plants were harvested as a bulk. Back- 2013 F₁ plants weregrown in Juana Diaz, PR and advanced cross using bulk based on event ofinterest selection. A backcross was made using a F₁ plant selection andA1088572 as the recurrent parent. BC₁F₁ plants were harvested as bulk.Back- 2013 BC₁F₁ plants were grown in Juana Diaz, PR and cross advancedusing plant selection for event of interest. A backcross was made usinga BC₁F₁ plant selection and A1088572 as the recurrent parent. BC₂F₁plants were harvested as bulk. Back- 2014 BC₂F₁ plants were grown inJuana Diaz, PR and cross advanced using plant selection for event ofinterest. A backcross was made using a BC₂F₁ plant selection andA1088572 as the recurrent parent. Individual plant selections werebulked as BC₃F₁. Back- 2014 BC₃F₁plants were grown in Juana Diaz, PR andcross advanced using plant selection for event of interest. A backcrosswas made using a BC₃F₁ plant selection and A1088572 as the recurrentparent. Individual plant selections were bulked as BC₄F₁. BC₄F₁ 2015BC₄F₁ plants were grown in Juana Diaz, PR and advanced using plantselection based on event of interest selection and MABC recovery of therecurrent parent. BC₄F₂ 2015 BC₄F₂ plants were grown in Juana Diaz, PRand advanced using plant selection based on homozygosity for theintended events. BC₄F₃ 2015 BC₄F₃ plants were grown in Juana Diaz, PRand advanced using plant selection based on homozygosity for theintended events. BC₄F₄ 2016 BC₄F₄ plants were grown in Juana Diaz, PRand advanced using bulk based on gene purity. Advanced Testing Gener-ation Year Selection F₅ 2017 Selected based on the lint yield, lintpercent, fiber quality. F₆ 2018 Selected based on the lint yield, lintpercent, fiber quality. F₇ 2019 Selected based on the lint yield, lintpercent, fiber quality.

The cotton variety 18R421B3XF has been judged to be uniform for breedingpurposes and testing; can be reproduced by planting and growing seeds ofthe variety under self-pollinating or sib-pollinating conditions, as isknown to those of skill in the agricultural arts; and shows no variantsother than what would normally be expected due to environment or thatwould occur for almost any characteristic during the course of repeatedsexual reproduction. The results of an objective description of thevariety are presented below in Table 1. Those of skill in the art willrecognize that these are typical values that may vary due to environmentand that other values that are substantially equivalent are within thescope of the invention.

TABLE 1 Phenotypic Description of Variety 18R421B3XF CHARACTERISTICVALUE AREAS OF ADAPTATION 1 Eastern 2 Delta 3 Central 4 Blacklands 5Plains 6 Western 7 Arizona GENERAL PLANT TYPE Plant Habit INTERMEDIATEFoliage INTERMEDIATE Stem Lodging ERECT Fruiting Branch NORMAL GrowthINTERMEDIATE Leaf Color MEDIUM GREEN Boll Shape LENGTH MORE THAN WIDTHBoll Breadth BROADEST AT MIDDLE MATURITY Days till maturity 124 PLANT cmto 1st Fruiting Branch 30.1 (from cotyledonary node) No. of Nodes to 1stFruiting Branch 6.2 (excluding cotyledonary node) Mature Plant Height incm 131.1 (from cotyledonary node to terminal) LEAF (Upper most fullyexpanded leaf) Type NORMAL Pubescence SPARSE Nectaries PRESENT STEM StemPubescence HAIRY GLANDS (Gossypol) Leaf NORMAL Stem NORMAL Calyx Lobe(normal is absent): NORMAL FLOWER Petals CREAM Pollen CREAM Petal SpotABSENT SEED Seed Index (g/100 seeds fuzzy basis) 9.41 Lint Index (glint/100 seeds) 6.39 BOLL Lint percent (%) Picked 40.59 Number of seedsper boll 31.61 Grams Seed Cotton per Boll 5.13 Number of Locules PerBoll 4 TO 5 Boll Type OPEN FIBER PROPERTIES Specify Method (HVI orother) HVI Length (inches 2.5% SL) 1.21 Uniformity (%) 82.98 Strength T1(g/tex) 30.49 Elongation E1 (%) 6.46 Micronaire 4.15 These are typicalvalues. Values may vary due to environment. Other values that aresubstantially equivalent are within the scope of the invention.

Cotton variety 18R421B3XF is a Bollgard® III XtendFlex® insect-protectedand herbicide-tolerant cotton variety, as a result of containing eventsCOT102, MON 15985, MON 88701, and MON 88913. Event COT102 protectsplants from feeding damage caused by lepidopteran insects by producingthe Bacillus thuringiensis strain AB88 VIP3A protein and is the subjectof U.S. Pat. No. 7,371,940. Event COT102 is also covered by one or moreof the following patents: U.S. Pat. Nos. 7,803,547 and 8,133,678. EventMON 15985 protects plants from feeding damage caused by lepidopteraninsects by producing Bacillus thuringiensis Cry1Ac and Cry2Ab proteinsand is the subject of U.S. Pat. No. 7,223,907, the disclosure of whichis incorporated herein by reference. Event MON 15985 is also covered byone or more of the following patents: U.S. Pat. Nos. 9,133,473;7,858,764; 7,700,830; 7,064,249; 6,943,282; 6,489,542; 5,728,925; and5,717,084. Event MON 88701 confers dicamba and glufosinate tolerance byproducing a dicamba monooxygenase from Stenotrophomonas maltophilia anda phosphinothricin acetyltransferase from Streptomyces hygroscopicus andis the subject of U.S. Pat. No. 8,735,661, the disclosure of which isincorporated herein by reference. Event MON 88701 is also covered by oneor more of the following patents: U.S. Pat. Nos. 9,024,115; 8,735,661;8,629,323; 8,420,888; 8,119,380; 7,939,721; 7,855,326; 7,812,224;7,112,665; 7,022,896; 5,850,019; 5,728,925; and 5,717,084 Event MON88913 confers glyphosate tolerance by producing a5-enolpyruvylshikimate-3-phosphate synthase protein from Agrobacteriumsp. strain CP4 and is the subject of U.S. Pat. No. 7,381,861, thedisclosure of which is incorporated herein by reference. Event MON 88913is also covered by one or more of the following patents: U.S. Pat. Nos.8,435,743; 8,071,735; 7,141,722; 7,112,725; 6,949,696; 6,660,911;6,083,878; 6,051,753; 5,728,925; and 5,717,084.

Breeding Cotton Variety 18R421B3Xf

One aspect of the current invention concerns methods for crossing thecotton variety 18R421B3XF with itself or a second plant and the seedsand plants produced by such methods. These methods can be used forpropagation of the cotton variety 18R421B3XF, or can be used to producehybrid cotton seeds and the plants grown therefrom. A hybrid plant canbe used as a recurrent parent at any given stage in a backcrossingprotocol during the production of a single locus conversion of thecotton variety 18R421B3XF.

The variety of the present invention is suited to the development of newvarieties based on the nature of the genetic background of the variety.In selecting a second plant to cross with 18R421B3XF for the purpose ofdeveloping novel cotton varieties, it will typically be desired tochoose plants that exhibit one or more selectable characteristics.Examples of selectable characteristics include, but are not limited to,higher fiber (lint) yield, earlier maturity, improved fiber quality,resistance to diseases and insects, tolerance to drought and heat, andimproved agronomic traits.

Any time the cotton variety 18R421B3XF is crossed with another,different, variety, first generation (F₁) cotton progeny are produced.The hybrid progeny are produced regardless of characteristics of the twoparental varieties used to produce the hybrid progeny. As such, an F₁hybrid cotton plant may be produced by crossing 18R421B3XF with anysecond cotton plant. The second cotton plant may be geneticallyhomogeneous, for example, inbred, or heterogeneous, for example, ahybrid. Any F₁ hybrid cotton plant produced by crossing cotton variety18R421B3XF with a second cotton plant is therefore a part of the presentinvention.

Cotton plants can be crossed, for example, by either natural ormechanical techniques. Natural pollination occurs in cotton either byself-pollination or natural cross-pollination, which typically is aidedby pollinating organisms. In either natural or artificial crosses,flowering and flowering time are important considerations.

The cotton flower is perfect in that the male and female structures arein the same flower. The crossed or hybrid seed can be produced by manualcrosses between selected parents. Floral buds of the parent that is tobe the female can be emasculated prior to the opening of the flower bymanual removal of the male anthers. At flowering, the pollen fromflowers of the parent plants designated as male, can be manually placedon the stigma of the previous emasculated flower. Seed developed fromthe cross is known as first generation (F₁) hybrid seed. Planting ofthis seed produces F₁ hybrid plants of which half their geneticcomponent is from the female parent and half from the male parent.Segregation of genes begins at meiosis thus producing second generation(F₂) seed. Assuming multiple genetic differences between the originalparents, each F₂ seed has a unique combination of genes.

Self-pollination occurs naturally in cotton with no manipulation of theflowers. For the crossing of two cotton plants, it may be beneficial touse artificial hybridization. In artificial hybridization, the flowerused as a female in a cross is manually cross-pollinated prior tomaturation of pollen from the flower, thereby preventingself-fertilization, or alternatively, the male parts of the flower canbe emasculated using a technique known in the art. Techniques foremasculating the male parts of a cotton flower include, for example,physical removal of the male parts, use of a genetic factor conferringmale sterility, and application of a chemical gametocide to the maleparts.

For artificial hybridization employing emasculation, flowers that areexpected to open the following day are selected on the female parent.The buds are swollen and the corolla is just visible through the calyxor has begun to emerge. Usually no more than two buds on a parent plantare prepared, and all self-pollinated flowers or immature buds areremoved with forceps. Special care is required to remove immature budsthat are hidden under the stipules at the leaf axil, and could developinto flowers at a later date. The flower is grasped between the thumband index finger and the location of the stigma determined by examiningthe sepals. The calyx is removed by grasping a sepal with the forceps,pulling it down and around the flower, and repeating the procedure untilthe five sepals are removed. The exposed corolla is removed with care toavoid injuring the stigma. Cross-pollination can then be carried outusing, for example, petri dishes or envelopes in which male flowers havebeen collected. Desiccators containing calcium chloride crystals can beused in some environments to dry male flowers to obtain adequate pollenshed.

Either with or without emasculation of the female flower, handpollination can be carried out by removing the stamens and pistil from aflower of the male parent with a forceps and gently brushing the anthersagainst the stigma of the female flower. Access to the stamens can beachieved by removing the front sepal and keel petals, or piercing thekeel with closed forceps and allowing them to open and push the petalsaway. Brushing the anthers on the stigma causes them to rupture, and thehighest percentage of successful crosses is obtained when pollen isclearly visible on the stigma. Pollen shed can be checked by tapping theanthers before brushing the stigma. Several male flowers may have to beused to obtain suitable pollen shed when conditions are unfavorable, orthe same male may be used to pollinate several flowers with good pollenshed.

Cross-pollination is more common within rows than between adjacent rows;therefore, it may be beneficial to grow populations with genetic malesterility on a square grid to create rows in all directions. Forexample, single-plant hills on 50-cm centers may be used, withsubdivision of the area into blocks of an equal number of hills forharvest from bulks of an equal amount of seed from male-sterile plantsin each block to enhance random pollination.

There are numerous steps in the development of any novel plantgermplasm. Plant breeding usually begins with the analysis andidentification of the problems and weaknesses of the current germplasm,the establishment of program goals, and the definition of breedingobjectives. The next step is selection of germplasm that possess thetraits that meet the program goals. The goal is typically to combine ina single variety a combination of selected traits from the parentalgermplasm. These traits may include, but are not limited to, resistanceto diseases and insects, tolerance to drought and heat, tolerance toherbicides, improvements in fiber traits, and agronomic traits.

Choice of breeding or selection methods depends on the mode of plantreproduction, the heritability of the selected trait(s), and the type ofvariety used commercially (e.g., F₁ hybrid variety, pureline variety,etc.). For heritable traits, especially highly heritable traits, achoice of individual plants evaluated at a single location will beeffective; whereas, for traits with low heritability, selection shouldbe based on mean values obtained from replicated evaluations of familiesof related plants. Popular selection methods commonly include, but arenot limited to, pedigree selection, modified pedigree selection, massselection, recurrent selection and backcrossing.

The complexity of inheritance typically influences the choice of thebreeding method. Backcross breeding is used to transfer one or moregenetic loci for a heritable trait into a variety. This approach can beused, for example, to breed disease-resistant plant varieties. Variousrecurrent selection techniques are used to improve quantitativelyinherited traits controlled by numerous genes. The use of recurrentselection in self-pollinating crops depends on the ease of pollination,the frequency of successful hybrids from each pollination, and thenumber of offspring from each cross.

Each breeding program may include an objective evaluation of theefficiency of the breeding procedure. Evaluation criteria vary dependingon the goal and objectives, but can include gain from selection per yearbased on comparisons to an appropriate standard, overall value of theadvanced breeding lines, and number of successful varieties produced perunit of input (e.g., per year, per dollar expended, etc.).

Promising advanced breeding lines are thoroughly tested and compared toappropriate standards in environments representative of the commercialtarget area(s) for generally three or more years. The best lines arecandidates for new commercial varieties, and those deficient in one ormore traits may be used as parents to produce new populations forfurther selection.

These processes, which lead to the final step of marketing anddistribution, may take as much as eight to 12 years from the time thefirst cross is made. Therefore, development of new varieties is atime-consuming process that requires precise forward planning, efficientuse of resources, and a minimum of changes in direction.

A most difficult task is the identification of individuals that aregenetically superior, because for most traits the true genotypic valueis masked by other confounding plant traits or environmental factors.One method of identifying these plants is to observe their performancerelative to other experimental plants and to one or more widely grownstandard varieties. Single observations are generally inconclusive,while replicated observations provide a better estimate of geneticworth.

The goal of plant breeding is to develop new, unique and superior cottonvarieties. The breeder selects and crosses two or more parental lines,followed by repeated selfing and selection that produces many newgenetic combinations. Each year, the plant breeder selects the germplasmto advance to the next generation. This germplasm is grown under uniqueand different geographical, climatic and soil conditions, and furtherselections are then made, during and at the end of the growing season.It is unpredictable which varieties will be eventually developed at theend of these processes. This unpredictability is because the breeder'sselection occurs in unique environments, with no control at the DNAlevel (using conventional breeding procedures), and yields millions ofdifferent possible genetic combinations. A breeder of ordinary skill inthe art cannot predict the final resulting lines he develops, exceptpossibly in a very gross and general fashion. The same breeder cannotproduce the same variety twice by using the exact same original parentsand the same selection techniques. This unpredictability results in theexpenditure of large amounts of research monies to develop novel cottonvarieties.

Pureline cultivars, such as generally used in cotton and many othercrops, are commonly bred by hybridization of two or more parentsfollowed by selection. The complexity of inheritance, the breedingobjectives and the available resources influence the breeding method.The development of new varieties requires development and selection, thecrossing of varieties and selection of progeny from superior crosses.

Pedigree breeding and recurrent selection breeding methods are used todevelop varieties from breeding populations. Breeding programs combinetraits from two or more varieties or various broad-based sources intobreeding pools from which varieties are developed by selfing andselection of phenotypes. The new varieties are evaluated to determinewhich have commercial potential.

Pedigree breeding can be used with self-pollinating crops. Two parentswhich possess favorable, complementary traits are crossed to produce anF₁. An F₂ population is produced by selfing one or several F₁ plants.Selection of individuals may begin in the F₂ population or laterdepending upon objectives of the breeder; then, beginning in the F₃,individuals from families can be selected. Replicated testing offamilies can begin in the F₃ or F₄ generation to improve theeffectiveness of selection for traits, especially those with lowheritability. At an advanced stage of inbreeding (i.e., F₆ and F₇), thelines or mixtures of phenotypically similar lines are typically testedfor potential release as new varieties.

Mass and recurrent selections can be used with either self- orcross-pollinating crops. A genetically variable population ofheterozygous individuals is either identified or created byintercrossing several different parents. Plants are selected based onindividual traits, outstanding progeny, or combining ability. Theselected plants are intercrossed to produce a new population for whichfurther cycles of selection are continued.

The single-seed descent procedure in the strict sense refers to plantinga segregating population, harvesting a sample of one seed per plant, andusing the one-seed samples to plant the next generation. When thepopulation has been advanced from the F₂ to the desired level ofinbreeding, the plants from which the lines are derived will each traceto different F₂ individuals. The number of plants in a populationdeclines each generation due to failure of some seeds to germinate orsome plants to produce at least one seed. As a result, not all of the F₂plants originally sampled in the population will be represented whengeneration advance is completed.

The modified single-seed descent procedures involve harvesting multipleseed, for example, using a single lock or a simple boll, from each plantin a population and combining them to form a bulk. Part of the bulk isused to plant the next generation and part is put in reserve. Thisprocedure has been used to save labor at harvest and to maintainadequate seed quantities of the population. The multiple-seed proceduremay be used to save labor. It is faster to gin bolls with a machine thanto remove one seed by hand. Using the multiple-seed procedure also makesit possible to plant the same number of seeds of a population eachgeneration of inbreeding, as enough seeds are harvested to make up forthe plants that did not germinate or produce seed.

Descriptions of other breeding methods that are commonly used fordifferent traits and crops can be found in one of several referencebooks (e.g., Allard, In: Principles of plant breeding, John Wiley &Sons, NY, University of California, Davis, Calif., 50-98, 1960;Simmonds, In: Principles of crop improvement, Longman, Inc., NY,369-399, 1979; Sneep and Hendriksen, In: Plant breeding perspectives,Wageningen (Ed), Center for Agricultural Publishing and Documentation,1979; Fehr, In: Principles of variety development, Theory and Technique(Vol 1) and Crop Species Soybean (Vol 2), Iowa State Univ., MacmillianPub. Co., NY, 360-376, 1987; Fehr, In: Soybeans: Improvement, Productionand Uses, 2d Ed., Manograph 16:249, 1987). Additionally, with any of themethods disclosed above, mutagenesis can be utilized to increase thediversity of the gene pool that is available in the breeding program.

Proper testing should detect faults and establish the level ofsuperiority or improvement over current varieties. In addition toshowing superior performance, there must be a demand for a new varietythat is compatible with industry standards or which creates a newmarket. The introduction of a new variety will incur additional costs tothe seed producer, the grower, processor and consumer; for specialadvertising and marketing, altered seed and commercial productionpractices, and new product utilization. The testing preceding release ofa new variety should take into consideration the research anddevelopment costs as well as the technical superiority of the finalvariety. For seed-propagated varieties, it must be feasible to produceseed easily and economically.

In addition to phenotypic observations, a plant can also becharacterized by its genotype. The genotype of a plant can be determinedby molecular marker profiling, which can be applied to plants of thesame variety or a related variety, and can reveal genetic differencesbetween plants, as well as between plant parts, which can be geneticallydifferent as a result of an event comprising, for example, a backcrossconversion, transgene, genetic sterility factor. Molecular markerprofiling can also be used to reveal or validate, for example, apedigree or genetic relationship among tested materials. Such molecularmarker profiling can be accomplished by using a variety of techniquesincluding, but not limited to, restriction fragment length polymorphism(RFLP), amplified fragment length polymorphism (AFLP), sequence-taggedsites (STS), randomly amplified polymorphic DNA (RAPD), arbitrarilyprimed polymerase chain reaction (AP-PCR), DNA amplificationfingerprinting (DAF), sequence characterized amplified regions (SCARs),variable number tandem repeat (VNTR), short tandem repeat (STR), singlefeature polymorphism (SFP), simple sequence length polymorphism (SSLP),restriction site associated DNA, allozymes, isozyme markers, singlenucleotide polymorphisms (SNPs), or simple sequence repeat (SSR)markers, also known as microsatellites (Gupta et al., 1999; Korzun etal., 2001). Various types of these marker platforms, for example, can beused to identify individual varieties developed from specific parentvarieties, as well as cells, or other plant parts thereof. See, forexample, Tyagi et al. (2014) “Genetic diversity and population structurein the US Upland cotton (Gossypium hirsutum L.),” Theoretical andApplied Genetics 127(2):283-295; Tatineni et al. (1996) “Geneticdiversity in elite cotton germplasm determined by morphologicalcharacteristics and RAPDs,” Crop Science 36(1):186-192; and Cho et al.(2014) “Genome-wide SNP marker panel applicable to Cotton Geneticdiversity test,” Proceedings of the International Cotton GenomeInitiative Conference 2(1):11, each of which are incorporated byreference herein in their entirety.

In some examples, one or more markers may be used to examine and/orevaluate genetic characteristics of a cotton variety. Particular markersused for these purposes are not limited to any particular set of markersand diagnostic platforms, but are envisioned to include any type ofmarkers and diagnostic platforms that can provide means fordistinguishing varieties. One method of genetic characterization may touse only homozygous loci for cotton variety 18R421B3XF.

Primers and PCR protocols for assaying these and other markers aredisclosed in, for example, CottonGen located on the World Wide Web atcottongen.org. In addition to being used for identification of cottonvariety 18R421B3XF, as well as plant parts and plant cells of cottonvariety 18R421B3XF, a genetic profile may be used to identify a cottonplant produced through the use of cotton variety 18R421B3XF or to verifya pedigree for progeny plants produced through the use of cotton variety18R421B3XF. A genetic marker profile may also be useful in breeding anddeveloping backcross conversions.

In an embodiment, the present invention provides a cotton plantcharacterized by molecular and physiological data obtained from arepresentative sample of said variety deposited with Provasoli-GuillardNational Center for Marine Algae and Microbiota (NCMA). Thus, plants,seeds, or parts thereof, having all or essentially all of themorphological and physiological characteristics of cotton variety18R421B3XF are provided. Further provided is a cotton plant formed bythe combination of the disclosed cotton plant or plant cell with anothercotton plant or cell and comprising the homozygous alleles of thevariety.

In some examples, a plant, a plant part, or a seed of cotton variety18R421B3XF may be characterized by producing a molecular profile. Amolecular profile may include, but is not limited to, one or moregenotypic and/or phenotypic profile(s). A genotypic profile may include,but is not limited to, a marker profile, such as a genetic map, alinkage map, a trait maker profile, a SNP profile, an SSR profile, agenome-wide marker profile, a haplotype, and the like. A molecularprofile may also be a nucleic acid sequence profile, and/or a physicalmap. A phenotypic profile may include, but is not limited to, a proteinexpression profile, a metabolic profile, an mRNA expression profile, andthe like.

One means of performing genetic marker profiling is using SSRpolymorphisms that are well known in the art. A marker system based onSSRs can be highly informative in linkage analysis relative to othermarker systems, in that multiple alleles for a given locus may bepresent. Another advantage of this type of marker is that through use offlanking primers, collecting more informative SSR data can be relativelyeasily achieved, for example, by using the polymerase chain reaction(PCR), thereby eliminating the need for labor-intensive Southernhybridization. PCR detection may be performed using two oligonucleotideprimers flanking the polymorphic segment of repetitive DNA to amplifythe SSR region.

Following amplification, genotype of test material revealed by eachmarker can be scored by electrophoresis of the amplification products.Scoring of marker genotype is based on the size of the amplifiedfragment, which correlates to the number of base pairs of the fragment.While variations in primers or laboratory procedures can affect thereported fragment size, the relative values should remain constant. Whencomparing multiple varieties, it may be beneficial to have all profilesperformed in the same lab. Primers that can be used are publicallyavailable and may be found in, for example, CottonGen (Yu et al.,CottonGen: a genomics, genetics and breeding database for cottonresearch,” Nucleic Acids Research 42 (D1):D1229-D1236, 2013).

A genotypic profile of cotton variety 18R421B3XF can be used to identifya plant comprising variety 18R421B3XF as a parent, since such plantswill comprise the same homozygous alleles as variety 18R421B3XF. Becausethe cotton variety at inbred stage is essentially homozygous at allrelevant loci, most loci should have only one type of allele present. Incontrast, a genetic marker profile of an F₁ progeny should be the sum ofthose parents. For example, if one parent was homozygous for allele X ata particular locus and the other parent homozygous for allele Y at thatlocus, the F₁ progeny will be XY (heterozygous) at that locus and thesubsequent generations of progeny produced by selection and breeding areexpected to be of genotype XX (homozygous), YY (homozygous), or XY(heterozygous) at that locus. When the F₁ plant is selfed or sibbed forsuccessive filial generations, that locus should be either XX or YY.

In addition, plants and plant parts substantially benefiting from theuse of variety 18R421B3XF in their development, such as variety18R421B3XF comprising a backcross conversion, transgene, or geneticsterility factor, may be identified by having a molecular marker profilewith a high percent identity to cotton variety 18R421B3XF. Such apercent identity might be 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%,99%, 99.5% or 99.9% identical to cotton variety 18R421B3XF.

A genotypic profile of variety 18R421B3XF also can be used to identifyessentially derived varieties and other progeny varieties developed fromthe use of variety 18R421B3XF, as well as cells and other plant partsthereof. Plants of the invention include any plant having at least 90%,91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 99.5%, or 99.9% of themarkers in the genotypic profile, and that retain 90%, 91%, 92%, 93%,94%, 95%, 96%, 97%, 98%, 99%, 99.5%, or 99.9% of the morphological andphysiological characteristics of variety 18R421B3XF when grown under thesame conditions. Such plants may be developed using markers well knownin the art. Progeny plants and plant parts produced using variety18R421B3XF may be identified, for example, by having a molecular markerprofile of at least 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%,75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%,89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 99.5% geneticcontribution from cotton variety 18R421B3XF, as measured by eitherpercent identity or percent similarity. Such progeny may be furthercharacterized as being within a pedigree distance of variety 18R421B3XF,such as within 1, 2, 3, 4, or 5 or less cross-pollinations to a cottonplant other than variety 18R421B3XF, or a plant that has variety18R421B3XF as a progenitor. Unique molecular profiles may be identifiedwith other molecular tools, such as SNPs and RFLPs.

The two cotton species commercially grown in the United States areGossypium hirsutum, commonly known as short staple or upland cotton andGossypium barbadense, commonly known as extra-long staple (ELS) or, inthe United States, as Pima cotton. Upland cotton fiber is used in a widearray of coarser spin count products. Pima cotton is used in finer spincount yarns (50-80) which are primarily used in more expensive garments.Other properties of Pima cotton are critical because of fiber end use.

Cotton is an important and valuable field crop. Thus, a continuing goalof plant breeders is to develop stable, high yielding cotton varietiesthat are agronomically sound. The reasons for this goal are obviously tomaximize the amount and quality of the fiber produced on the land usedand to supply fiber, oil and food for animals and humans. To accomplishthis goal, the cotton breeder must select and develop plants that havethe traits that result in superior cultivars.

Improvement of Cotton Varieties

In certain further aspects, the invention provides plants modified toinclude at least a first trait. Such plants may, in one embodiment, bedeveloped by a plant breeding technique called backcrossing, whereinessentially all of the morphological and physiological characteristicsof a variety are recovered in addition to a genetic locus transferredinto the hybrid via the backcrossing technique. The term backcrossing asused herein refers to the repeated crossing of a hybrid progeny back toa starting variety into which introduction of a trait is being carriedout. The parental plant which contributes the locus or loci for a traitis termed the nonrecurrent or donor parent. This terminology refers tothe fact that the nonrecurrent parent is used one time in the backcrossprotocol and therefore does not recur.

The parental cotton plant to which the locus or loci from thenonrecurrent parent are transferred is known as the recurrent parent asit is used for several rounds in the backcrossing protocol (Poehlman andSleper, In: Breeding Field Crops, Iowa State University Press, Ames,1995; Sprague and Dudley, In: Corn and Improvement, 3rd ed., 1988; Fehr,In: Principles of variety development, Theory and Technique (Vol 1) andCrop Species Soybean (Vol 2), Iowa State Univ., Macmillian Pub. Co., NY,360-376, 1987b; Fehr, In: Soybeans: Improvement, Production and Uses, 2dEd., Manograph 16:249, 1987). In a typical backcross protocol, theoriginal line of interest (recurrent parent) is crossed to a secondvariety (nonrecurrent parent) that carries the genetic locus to betransferred. The resulting progeny from this cross are then crossedagain to the recurrent parent and the process is repeated until a cottonplant is obtained wherein essentially all of the morphological andphysiological characteristics of the recurrent parent are recovered inthe converted plant, in addition to the transferred locus from thenonrecurrent parent.

The backcross process may be accelerated by the use of genetic markers,such as Simple Sequence Length Polymorphisms (SSLPs) (Williams et al.,Nucleic Acids Res., 18:6531-6535, 1990), Randomly Amplified PolymorphicDNAs (RAPDs), DNA Amplification Fingerprinting (DAF), SequenceCharacterized Amplified Regions (SCARs), Arbitrary Primed PolymeraseChain Reaction (AP-PCR), Amplified Fragment Length Polymorphisms (AFLPs)(EP 534 858, specifically incorporated herein by reference in itsentirety), and Single Nucleotide Polymorphisms (SNPs) (Wang et al.,Science, 280:1077-1082, 1998) to identify plants with the greatestgenetic complement from the recurrent parent.

The selection of a suitable recurrent parent is an important step for asuccessful backcrossing procedure. The goal of a backcross protocol isto add or substitute one or more new traits in a variety. To accomplishthis, a genetic locus of the recurrent parent is modified or substitutedwith a locus from the nonrecurrent parent, while retaining essentiallyall of the rest of the genetic, and therefore the morphological andphysiological constitution of the original variety. The choice of theparticular nonrecurrent parent will depend on the purpose of thebackcross; one possible purpose is to add some commercially relevant,agronomic trait to the plant. The exact backcrossing protocol willdepend on the characteristic or trait being altered to determine anappropriate testing protocol. Although backcrossing methods aresimplified when the characteristic being transferred is a dominantallele, a recessive allele may also be transferred. In this instance itmay be necessary to introduce a test of the progeny to determine if thecharacteristic has been transferred.

Many traits have been identified that are not regularly selected for inthe development of a new variety but that can be improved bybackcrossing techniques. A genetic locus conferring the traits may ormay not be transgenic. Examples of such traits known to those of skillin the art include, but are not limited to, male sterility, herbicidetolerance, resistance for bacterial, fungal, or viral disease, insect ornematode resistance, male sterility, ease of transformation, resistanceto abiotic stresses and improved fiber characteristics. These genes aregenerally inherited through the nucleus, but may be inherited throughthe cytoplasm.

Direct selection may be applied where a genetic locus acts as a dominanttrait. An example of a dominant trait is the herbicide tolerance trait.For this selection process, the progeny of the initial cross are sprayedwith the herbicide prior to the backcrossing. The spraying eliminatesany plants which do not have the herbicide tolerance characteristic, andonly those plants which have the herbicide tolerance gene are used inthe subsequent backcross. This process is then repeated for alladditional backcross generations.

Many useful traits are those which are introduced by genetictransformation techniques. Methods for the genetic transformation ofcotton are known to those of skill in the art, (see, e. g. Firoozabadyet al., Plant Mol. Biol., 10:105-116, 1987). For example, broadlyapplicable plant transformation methods which have been describedinclude Agrobacterium-mediated transformation, microprojectilebombardment, electroporation, and direct DNA uptake by protoplasts.

Agrobacterium-mediated transfer is a widely applicable system forintroducing gene loci into plant cells, including cotton. An advantageof the technique is that DNA can be introduced into whole plant tissues,thereby bypassing the need for regeneration of an intact plant from aprotoplast. Modern Agrobacterium transformation vectors are capable ofreplication in E. coli as well as Agrobacterium, allowing for convenientmanipulations (Klee et al., Bio. Tech., 3(7):637-642, 1985). Moreover,recent technological advances in vectors for Agrobacterium-mediated genetransfer have improved the arrangement of genes and restriction sites inthe vectors to facilitate the construction of vectors capable ofexpressing various polypeptide coding genes. The vectors described haveconvenient multi-linker regions flanked by a promoter and apolyadenylation site for direct expression of inserted polypeptidecoding genes. Additionally, Agrobacterium containing both armed anddisarmed Ti genes can be used for transformation.

In those plant strains where Agrobacterium-mediated transformation isefficient, it is the method of choice because of the facile and definednature of the gene locus transfer. The use of Agrobacterium-mediatedplant integrating vectors to introduce DNA into plant cells is wellknown in the art (Fraley et al., Bio. Tech., 3(7):629-635, 1985; U.S.Pat. No. 5,563,055). One efficient means for transformation of cotton inparticular is transformation and regeneration of cotton hypocotylexplants following inoculation with Agrobacterium tumefaciens fromprimary callus development, embryogenesis, embryogenic callusidentification, transgenic cotton shoot production and the developmentof transgenic plants, as is known in the art.

To effect transformation by electroporation, for example, one may employeither friable tissues, such as a suspension culture of cells orembryogenic callus or alternatively one may transform immature embryosor other organized tissue directly. In this technique, one wouldpartially degrade the cell walls of the chosen cells by exposing them topectin-degrading enzymes (pectolyases) or mechanically wound tissues ina controlled manner. Protoplasts may also be employed forelectroporation transformation of plants (Bates, Mol. Biotechnol.,2(2):135-145, 1994; Lazzeri, Methods Mol. Biol., 49:95-106, 1995). Forexample, the generation of transgenic cotyledon-derived protoplasts wasdescribed by Dhir and Widholm in Intl. Patent Appl. Publ. No. WO92/17598, the disclosure of which is specifically incorporated herein byreference. When protoplasts are used, transformation can also beachieved using methods based on calcium phosphate precipitation,polyethylene glycol treatment, and combinations of these treatments(see, e.g., Potrykus et al., Mol. Gen. Genet., 199(2):169-177, 1985;Omirulleh et al., Plant Mol. Biol., 21(3):415-428, 1993; Fromm et al.,Nature, 319(6056):791-793, 1986; Uchimiya et al., Mol. Gen. Genet.,204(2):204-207, 1986; Marcotte and Bayley, Nature, 335(6189):454-457,1988).

Microprojectile bombardment is another efficient method for deliveringtransforming DNA segments to plant cells. In this method, particles arecoated with nucleic acids and delivered into cells by a propellingforce. Exemplary particles include those comprised of tungsten,platinum, and often, gold. For the bombardment, cells in suspension areconcentrated on filters or solid culture medium. Alternatively, immatureembryos or other target cells may be arranged on solid culture medium.The cells to be bombarded are positioned at an appropriate distancebelow the macroprojectile stopping plate.

Microprojectile bombardment techniques are widely applicable, and may beused to transform virtually any plant species. The application ofmicroprojectile bombardment for the transformation of cotton isdescribed, for example, in Rajasekaran et al., Mol. Breed., 2:307-319,1996. An illustrative embodiment of a method for microprojectilebombardment is the Biolistics Particle Delivery System, which can beused to propel particles coated with DNA or cells through a screen, suchas a stainless steel or Nytex screen, onto a surface covered with targetcells. The screen disperses the particles so that they are not deliveredto the recipient cells in large aggregates. It is believed that a screenintervening between the projectile apparatus and the cells to bebombarded reduces the size of projectiles aggregate and may contributeto a higher frequency of transformation by reducing the damage inflictedon the recipient cells by projectiles that are too large.

Included among various plant transformation techniques are methodspermitting the site-specific modification of a plant genome. Thesemodifications can include, but are not limited to, site-specificmutations, deletions, insertions, and replacements of nucleotides. Thesemodifications can be made anywhere within the genome of a plant, forexample, in genomic elements, including, among others, coding sequences,regulatory elements, and non-coding DNA sequences. Any number of suchmodifications can be made and that number of modifications may be madein any order or combination, for example, simultaneously all together orone after another. Such methods may lead to changes in phenotype. Thetechniques for such modifications are well known in the art and include,for example, use of CRISPR-Cas systems, zinc-finger nucleases (ZFNs),and transcription activator-like effector nucleases (TALENs), amongothers.

It is understood to those of skill in the art that a locus of transgenicorigin need not be directly transformed into a plant, as techniques forthe production of stably transformed cotton plants that pass single locito progeny by Mendelian inheritance is well known in the art. Suchsingle loci may therefore be passed from parent plant to progeny plantsby standard plant breeding techniques that are well known in the art.Non-limiting examples of traits that may be introduced directly or bybackcrossing are presented below.

A. Male Sterility

Male sterility genes can increase the efficiency with which hybrids aremade, in that they eliminate the need to physically emasculate the plantused as a female in a given cross. Where one desires to employmale-sterility systems, it may be beneficial to also utilize one or moremale-fertility restorer genes. For example, where cytoplasmic malesterility (CMS) is used, hybrid crossing requires three inbred lines:(1) a cytoplasmically male-sterile line having a CMS cytoplasm; (2) afertile inbred with normal cytoplasm, which is isogenic with the CMSline for nuclear genes (“maintainer line”); and (3) a distinct, fertileinbred with normal cytoplasm, carrying a fertility restoring gene(“restorer” line). The CMS line is propagated by pollination with themaintainer line, with all of the progeny being male sterile, as the CMScytoplasm is derived from the female parent. These male sterile plantscan then be efficiently employed as the female parent in hybrid crosseswith the restorer line, without the need for physical emasculation ofthe male reproductive parts of the female parent.

The presence of a male-fertility restorer gene results in the productionof fully fertile F₁ hybrid progeny. If no restorer gene is present inthe male parent, male-sterile hybrids are obtained. Examples ofmale-sterility genes and corresponding restorers which could be employedwith the plants of the invention are well known to those of skill in theart of plant breeding. Examples of such genes include CMS-D2-2, CMS-hir,CMS-D8, CMS-D4, and CMS-C1. Fertility can be restored to CMS-D2-2 by theD2 restorer in which the restorer factor(s) was introduced from thegenome of G. harknessii Brandegee (D2-2). Microsporogenesis in both CMSsystems aborts during the premeiotic stage. One dominant restorer genefrom the D8 restorer was identified to restore fertility of CMS-D8. TheD2 restorer for CMS-D2-2 also restores the fertility of CMS-D8, CMS-hir,and CMS-C1.

B. Herbicide Tolerance

Numerous herbicide tolerance genes are known and may be employed withthe invention. A non-limiting example is a gene conferring resistance toa herbicide that inhibits the growing point or meristem such asimidazolinone or sulfonylurea herbicides. As imidazolinone andsulfonylurea herbicides are acetolactate synthase (ALS)-inhibitingherbicides that prevent the formation of branched chain amino acids,exemplary genes in this category code for ALS and AHAS enzymes asdescribed, for example, by Lee et al., EMBO J., 7:1241, 1988; Gleen etal., Plant Molec. Biology, 18:1185, 1992; and Miki et al., Theor. Appl.Genet., 80:449, 1990. As a non-limiting example, a gene may be employedto confer resistance to the exemplary sulfonylurea herbicidenicosulfuron.

Resistance genes for glyphosate (resistance conferred by mutant5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) and aroA genes,respectively) and other phosphono compounds such as glufosinate(phosphinothricin acetyltransferase (PAT) and Streptomyces hygroscopicusphosphinothricin acetyltransferase (bar) genes) may also be used. See,for example, U.S. Pat. No. 4,940,835 to Shah et al., which discloses thenucleotide sequence of a form of EPSPS that can confer glyphosateresistance. Non-limiting examples of EPSPS transformation eventsconferring glyphosate resistance are provided by U.S. Pat. Nos.6,040,497 and 7,632,985. The MON89788 event disclosed in U.S. Pat. No.7,632,985 in particular is beneficial in conferring glyphosate tolerancein combination with an increase in average yield relative to priorevents.

A DNA molecule encoding a mutant aroA gene can be obtained under ATCCAccession No. 39256, and the nucleotide sequence of the mutant gene isdisclosed in U.S. Pat. No. 4,769,061 to Comai. A hygromycin Bphosphotransferase gene from E. coli that confers resistance toglyphosate in tobacco callus and plants is described in Penaloza-Vazquezet al., Plant Cell Reports, 14:482, 1995. European Patent ApplicationPublication No. EP0333033 to Kumada et al., and U.S. Pat. No. 4,975,374to Goodman et al., disclose nucleotide sequences of glutamine synthetasegenes that confer resistance to herbicides such as L-phosphinothricin.The nucleotide sequence of a phosphinothricin acetyltransferase gene isprovided in European Patent Application Publication No. EP0242246 toLeemans et al. DeGreef et al. (Biotechnology, 7:61, 1989) describe theproduction of transgenic plants that express chimeric bar genes codingfor phosphinothricin acetyl transferase activity. Exemplary genesconferring resistance to a phenoxy class herbicide haloxyfop and acyclohexanedione class herbicide sethoxydim are the Acct-S1, Acct-S2 andAcct-S3 genes described by Marshall et al., (Theor. Appl. Genet.,83:435, 1992). As a non-limiting example, a gene may confer resistanceto other exemplary phenoxy class herbicides that include, but are notlimited to, quizalofop-p-ethyl and 2,4-dichlorophenoxyacetic acid(2,4-D).

Genes are also known that confer resistance to herbicides that inhibitphotosynthesis such as, for example, triazine herbicides (psbA and gs+genes) and benzonitrile herbicides (nitrilase gene). As a non-limitingexample, a gene may confer resistance to the exemplary benzonitrileherbicide bromoxynil. Przibila et al. (Plant Cell, 3:169, 1991) describethe transformation of Chlamydomonas with plasmids encoding mutant psbAgenes. Nucleotide sequences for nitrilase genes are disclosed in U.S.Pat. No. 4,810,648 to Stalker, and DNA molecules containing these genesare available under ATCC Accession Nos. 53435, 67441, and 67442. Cloningand expression of DNA coding for a glutathione S-transferase isdescribed by Hayes et al. (Biochem. J., 285:173, 1992).4-hydroxyphenylpyruvate dioxygenase (HPPD) is a target of theHPPD-inhibiting herbicides, which deplete plant plastoquinone andvitamin E pools. Rippert et al. (Plant Physiol., 134:92, 2004) describesan HPPD-inhibitor resistant tobacco plant that was transformed with ayeast-derived prephenate dehydrogenase (PDH) gene. Protoporphyrinogenoxidase (PPO) is the target of the PPO-inhibitor class of herbicides; aPPO-inhibitor resistant PPO gene was recently identified in Amaranthustuberculatus (Patzoldt et al., PNAS, 103(33):12329, 2006). The herbicidemethyl viologen inhibits CO2 assimilation. Foyer et al. (Plant Physiol.,109:1047, 1995) describe a plant overexpressing glutathione reductase(GR) that is resistant to methyl viologen treatment.

Siminszky (Phytochemistry Reviews, 5:445, 2006) describes plantcytochrome P450-mediated detoxification of multiple, chemicallyunrelated classes of herbicides. Modified bacterial genes have beensuccessfully demonstrated to confer resistance to atrazine, a herbicidethat binds to the plastoquinone-binding membrane protein QB inphotosystem II to inhibit electron transport. See, for example, studiesby Cheung et al. (PNAS, 85:391, 1988), describing tobacco plantsexpressing the chloroplast psbA gene from an atrazine-resistant biotypeof Amaranthus hybridus fused to the regulatory sequences of a nucleargene, and Wang et al. (Plant Biotech. J., 3:475, 2005), describingtransgenic alfalfa, Arabidopsis, and tobacco plants expressing the atzAgene from Pseudomonas sp. that were able to detoxify atrazine.

Bayley et al. (Theor. Appl. Genet., 83:645, 1992) describe the creationof 2,4-D-resistant transgenic tobacco and cotton plants using the 2,4-Dmonooxygenase gene tfdA from Alcaligenes eutrophus plasmid pJP5. U.S.Patent Application Publication No. 20030135879 describes the isolationof a gene for dicamba monooxygenase (DMO) from Pseudomonas maltophiliathat is involved in the conversion of dicamba to a non-toxic3,6-dichlorosalicylic acid and thus may be used for producing plantstolerant to this herbicide.

Other examples of herbicide resistance have been described, forinstance, in U.S. Pat. Nos. 6,803,501; 6,448,476; 6,248,876; 6,225,114;6,107,549; 5,866,775; 5,804,425; 5,633,435; 5,463,175.

C. Disease Resistance

Plant defenses are often activated by specific interaction between theproduct of a disease resistance gene (R) in the plant and the product ofa corresponding avirulence (Avr) gene in the pathogen. A plant line canbe transformed with cloned resistance gene to engineer plants that areresistant to specific pathogen strains. See, for example Jones et al.,Science, 266:789, 1994 (cloning of the tomato Cf-9 gene for resistanceto Cladosporium fulvum); Martin et al., Science, 262:1432, 1993 (tomatoPto gene for resistance to Pseudomonas syringae pv.); Mindrinos et al.,Cell, 78:1089, 1994 (Arabidopsis RPS2 gene for resistance to Pseudomonassyringae). Logemann et al., (Bio/technology, 10:305, 1992), for example,disclose transgenic plants expressing a barley ribosome-inactivatinggene have an increased resistance to fungal disease.

A viral-invasive protein or a complex toxin derived therefrom may alsobe used for viral disease resistance. For example, the accumulation ofviral coat proteins in transformed plant cells imparts resistance toviral infection and/or disease development effected by the virus fromwhich the coat protein gene is derived, as well as by related viruses.See Beachy et al., Ann. Rev. Phytopathol., 28:451, 1990. Coatprotein-mediated resistance has been conferred upon transformed plantsagainst alfalfa mosaic virus, cucumber mosaic virus, tobacco streakvirus, potato virus X, potato virus Y, tobacco etch virus, tobaccorattle virus and tobacco mosaic virus.

A virus-specific antibody may also be used. See, for example,Tavladoraki et al., (Nature, 366:469, 1993), who show that transgenicplants expressing recombinant antibody genes are protected from virusattack. Additional means of inducing whole-plant resistance to apathogen include modulation of the systemic acquired resistance (SAR) orpathogenesis related (PR) genes, for example genes homologous to theArabidopsis thaliana NIM1/NPR1/SAI1, and/or increasing salicylic acidproduction (Ryals et al., Plant Cell, 8:1809-1819, 1996).

Plant defensins may be used to provide resistance to fungal pathogens(Thomma et al., Planta, 216:193-202, 2002).

Nematode resistance has been described, for example, in U.S. Pat. No.6,228,992 and bacterial disease resistance in U.S. Pat. No. 5,516,671.

D. Insect Resistance

One example of an insect resistance gene includes a Bacillusthuringiensis protein, a derivative thereof, or a synthetic polypeptidemodeled thereon. See, for example, Geiser et al., (Gene, 48:109, 1986),who disclose the cloning and nucleotide sequence of a Bt δ-endotoxingene. Moreover, DNA molecules encoding δ-endotoxin genes can bepurchased from the American Type Culture Collection, Manassas, Va., forexample, under ATCC Accession Nos. 40098, 67136, 31995 and 31998.Another example is a lectin. See, for example, Van Damme et al., (PlantMolec. Biol., 24:25, 1994), who disclose the nucleotide sequences ofseveral Clivia miniata mannose-binding lectin genes. A vitamin-bindingprotein may also be used, such as avidin. See PCT applicationUS93/06487, the contents of which are hereby incorporated by reference.This application teaches the use of avidin and avidin homologues aslarvicides against insect pests.

Yet another insect resistance gene is an enzyme inhibitor, for example,a protease or proteinase inhibitor or an amylase inhibitor. See, forexample, Abe et al., J. Biol. Chem., 262:16793, 1987 (nucleotidesequence of rice cysteine proteinase inhibitor), Huub et al., PlantMolec. Biol., 21:985, 1993 (nucleotide sequence of cDNA encoding tobaccoproteinase inhibitor I), and Sumitani et al., Biosci. Biotech. Biochem.,57:1243, 1993 (nucleotide sequence of Streptomyces nitrosporeusα-amylase inhibitor).

An insect-specific hormone or pheromone may also be used. See, forexample, Hammock et al., (Nature, 344:458, 1990) disclosing baculovirusexpression of cloned juvenile hormone esterase, an inactivator ofjuvenile hormone, Gade and Goldsworthy (Eds. Physiological System inInsects, Elsevier Academic Press, Burlington, Mass., 2007), describingallostatins and their potential use in pest control; and Palli et al.(Vitam. Horm., 73:59-100, 2005), disclosing use of ecdysteroid andecdysteroid receptor in agriculture. The diuretic hormone receptor (DHR)was identified in Price et al. (Insect Mol. Biol., 13:469-480, 2004) asa candidate target of insecticides.

Still other examples include an insect-specific antibody or animmunotoxin derived therefrom and a developmental-arrestive protein. SeeTaylor et al., (Seventh Int'l Symposium on Molecular Plant-MicrobeInteractions (Edinburgh, Scotland) Abstract #497, 1994), who describedenzymatic inactivation in transgenic tobacco via production ofsingle-chain antibody fragments.

E. Resistance to Abiotic Stresses

Abiotic stress includes dehydration or other osmotic stress, salinity,high or low light intensity, high or low temperatures, submergence,exposure to heavy metals, and oxidative stress.Delta-pyrroline-5-carboxylate synthetase (P5CS) from mothbean has beenused to provide protection against general osmotic stress.Mannitol-1-phosphate dehydrogenase (mt1D) from E. coli has been used toprovide protection against drought and salinity. Choline oxidase (codAfrom Arthrobactor globiformis) can protect against cold and salt. E.coli choline dehydrogenase (betA) provides protection against salt.Additional protection from cold can be provided by omega-3-fatty aciddesaturase (fad7) from Arabidopsis thaliana. Trehalose-6-phosphatesynthase and levansucrase (SacB) from yeast and Bacillus subtilis,respectively, can provide protection against drought (summarized fromAnnex II Genetic Engineering for Abiotic Stress Tolerance in Plants,Consultative Group On International Agricultural Research TechnicalAdvisory Committee). Overexpression of superoxide dismutase can be usedto protect against superoxides, as described in U.S. Pat. No. 5,538,878to Thomas et al.

F. Modified Fatty Acid, Phytate, and Carbohydrate Metabolism

Genes may be used conferring modified fatty acid metabolism. Forexample, stearyl-ACP desaturase genes may be used. See Knutzon et al.,Proc. Natl. Acad. Sci. USA, 89:2624, 1992. Various fatty aciddesaturases have also been described, such as a Saccharomyces cerevisiaeOLE1 gene encoding delta-9 fatty acid desaturase, an enzyme which formsthe monounsaturated palmitoleic (16:1) and oleic (18:1) fatty acids frompalmitoyl (16:0) or stearoyl (18:0) CoA (McDonough et al., J. Biol.Chem., 267(9):5931-5936, 1992); a gene encoding a stearoyl-acyl carrierprotein Δ9 desaturase from castor (Fox et al. Proc. Natl. Acad. Sci.USA, 90(6):2486-2490, 1993); Δ6 and Δ12 desaturases from thecyanobacteria Synechocystis responsible for the conversion of linoleicacid (18:2) to gamma-linolenic acid (18:3 gamma) (Reddy et al. PlantMol. Biol., 22(2):293-300, 1993); a gene from Arabidopsis thaliana thatencodes an omega-3 desaturase (Arondel et al. Science,258(5086):1353-1355, 1992); plant 49 desaturases (PCT Application Publ.No. WO 91/13972) and soybean and Brassica 415 desaturases (EuropeanPatent Application Publ. No. EP 0616644).

Phytate metabolism may also be modified by introduction of aphytase-encoding gene to enhance breakdown of phytate, adding more freephosphate to the transformed plant. For example, see Van Hartingsveldtet al., (Gene, 127:87, 1993), for a disclosure of the nucleotidesequence of an Aspergillus niger phytase gene. This, for example, couldbe accomplished by cloning and then reintroducing DNA associated withthe single allele which is responsible for mutants characterized by lowlevels of phytic acid. See Raboy et al., (Maydica, 35:383, 1990).

A number of genes are known that may be used to alter carbohydratemetabolism. For example, plants may be transformed with a gene codingfor an enzyme that alters the branching pattern of starch. See Shirozaet al., J. Bacteol., 170:810, 1988 (nucleotide sequence of Streptococcusmutans fructosyltransferase gene), Steinmetz et al., Mol. Gen. Genet.,20:220, 1985 (nucleotide sequence of Bacillus subtilis levansucrasegene), Pen et al., BioTechnology, 10:292, 1992 (production of transgenicplants that express Bacillus licheniformis α-amylase), Elliot et al.,Plant Molec. Biol., 21:515, 1993 (nucleotide sequences of tomatoinvertase genes), Sergaard et al., J. Biol. Chem., 268:22480, 1993(site-directed mutagenesis of barley α-amylase gene), and Fisher et al.,Plant Physiol., 102:1045, 1993 (maize endosperm starch branching enzymeII). The Z10 gene encoding a 10 kD zein storage protein from maize mayalso be used to alter the quantities of 10 kD zein in the cells relativeto other components (Kirihara et al., Mol. Gen. Genet., 211:477-484,1988).

G. Improved Cotton Fiber Characteristics

Fiber characteristics such as fiber quality of quantity representanother example of a trait that may be modified in cotton varieties. Forexample, U.S. Pat. No. 6,472,588 describes transgenic cotton plantstransformed with a sucrose phosphate synthase nucleic acid to alterfiber characteristics such as strength, length, fiber fineness, fibermaturity ratio, immature fiber content, fiber uniformity, andmicronaire. Cotton plants comprising one or more genes coding for anenzyme selected from the group consisting of endoxyloglucan transferase,catalase and peroxidase for the improvement of cotton fibercharacteristics are also described in U.S. Pat. No. 6,563,022. Cottonmodification using ovary-tissue transcriptional factors preferentiallydirecting gene expression in ovary tissue, particularly in very earlyfruit development, utilized to express genes encoding isopentenyltransferase in cotton ovule tissue and modify the characteristics ofboll set in cotton plants and alter fiber quality characteristicsincluding fiber dimension and strength is discussed in U.S. Pat. No.6,329,570. A gene controlling the fiber formation mechanism in cottonplants is described in U.S. Pat. No. 6,169,174.

Genes involved in lignin biosynthesis are described by Dwivedi et al.,Mol. Biol., 26:61-71, 1994; Tsai et al., Physiol., 107:1459, 1995; U.S.Pat. No. 5,451,514 (claiming the use of cinnamyl alcohol dehydrogenasegene in an antisense orientation such that the endogenous plant cinnamylalcohol dehydrogenase gene is inhibited).

H. Additional Traits

Additional traits can be introduced into the cotton variety of thepresent invention. A non-limiting example of such a trait is a codingsequence which decreases RNA and/or protein levels. The decreased RNAand/or protein levels may be achieved through RNAi methods, such asthose described in U.S. Pat. No. 6,506,559 to Fire and Mellow.

Another trait that may find use with the cotton variety of the inventionis a sequence which allows for site-specific recombination. Examples ofsuch sequences include the FRT sequence, used with the FLP recombinase(Zhu and Sadowski, J. Biol. Chem., 270:23044-23054, 1995); and the LOXsequence, used with CRE recombinase (Sauer, Mol. Cell. Biol.,7:2087-2096, 1987). The recombinase genes can be encoded at any locationwithin the genome of the cotton plant, and are active in the hemizygousstate.

It may also be desirable to make cotton plants more tolerant to or moreeasily transformed with Agrobacterium tumefaciens. Expression of p53 andiap, two baculovirus cell-death suppressor genes, inhibited tissuenecrosis and DNA cleavage. Additional targets can include plant-encodedproteins that interact with the Agrobacterium Vir genes; enzymesinvolved in plant cell wall formation; and histones, histoneacetyltransferases and histone deacetylases (reviewed in Gelvin,Microbiology & Mol. Biol. Reviews, 67:16-37, 2003).

Tissue Cultures and In Vitro Regeneration of Cotton Plants

A further aspect of the invention relates to tissue cultures of thecotton variety designated 18R421B3XF. As used herein, the term “tissueculture” indicates a composition comprising isolated cells of the sameor a different type or a collection of such cells organized into partsof a plant. Exemplary types of tissue cultures are protoplasts, calliand plant cells that are intact in plants or parts of plants, such asembryos, pollen, flowers, leaves, roots, root tips, anthers, and thelike. In one embodiment, the tissue culture comprises embryos,protoplasts, meristematic cells, pollen, leaves or anthers.

An important ability of a tissue culture is the capability to regeneratefertile plants. This allows, for example, transformation of the tissueculture cells followed by regeneration of transgenic plants. Fortransformation to be efficient and successful, DNA must be introducedinto cells that give rise to plants or germ-line tissue.

Plants typically are regenerated via two distinct processes; shootmorphogenesis and somatic embryogenesis. Shoot morphogenesis is theprocess of shoot meristem organization and development. Shoots grow outfrom a source tissue and are excised and rooted to obtain an intactplant. During somatic embryogenesis, an embryo (similar to the zygoticembryo), containing both shoot and root axes, is formed from somaticplant tissue. An intact plant rather than a rooted shoot results fromthe germination of the somatic embryo.

Shoot morphogenesis and somatic embryogenesis are different processesand the specific route of regeneration is primarily dependent on theexplant source and media used for tissue culture manipulations. Whilethe systems are different, both systems show variety-specific responseswhere some lines are more responsive to tissue culture manipulationsthan others. A line that is highly responsive in shoot morphogenesis maynot generate many somatic embryos. Lines that produce large numbers ofembryos during an induction step may not give rise to rapidly-growingproliferative cultures. Therefore, it may be desired to optimize tissueculture conditions for each cotton line. These optimizations may readilybe carried out by one of skill in the art of tissue culture throughsmall-scale culture studies. In addition to line-specific responses,proliferative cultures can be observed with both shoot morphogenesis andsomatic embryogenesis. Proliferation is beneficial for both systems, asit allows a single, transformed cell to multiply to the point that itwill contribute to germ-line tissue.

Embryogenic cultures can also be used successfully for regeneration,including regeneration of transgenic plants, if the origin of theembryos is recognized and the biological limitations of proliferativeembryogenic cultures are understood. Biological limitations include thedifficulty in developing proliferative embryogenic cultures and reducedfertility problems (culture-induced variation) associated with plantsregenerated from long-term proliferative embryogenic cultures. Some ofthese problems are accentuated in prolonged cultures. The use of morerecently cultured cells may decrease or eliminate such problems.

Definitions

In the description and tables herein, a number of terms are used. Inorder to provide a clear and consistent understanding of thespecification and claims, the following definitions are provided:

A: When used in conjunction with the word “comprising” or other openlanguage in the claims, the words “a” and “an” denote “one or more.”

Agronomic Characteristics: Characteristics, which will vary fromcrop-to-crop and plant-to-plant, such as yield, maturity, pestresistance, and lint percent, and are relevant to the commercial successof a crop or plant. For example, agronomic characteristics for cottoninclude, but are not limited to, improved yield, maturity, fibercontent, and fiber qualities.

Allele: Any of one or more alternative forms of a genetic locus. In adiploid cell or organism, the two alleles of a given gene occupysyntenic loci on a pair of homologous chromosomes.

Backcrossing: A process in which a breeder repeatedly crosses hybridprogeny, for example a first generation hybrid (F₁), back to one of theparents of the hybrid progeny. Backcrossing can be used to introduce oneor more single locus conversions from one genetic background intoanother.

Crossing: The mating of two parent plants.

Cross-pollination: Fertilization by the union of two gametes fromdifferent plants.

Diploid: A cell or organism having two sets of chromosomes.

Disease Resistance: The ability of plants to restrict the activities ofa specified pest, such as an insect, fungus, virus, or bacteria.

Disease Tolerance: The ability of plants to endure a specified pest(such as an insect, fungus, virus or bacteria) or an adverseenvironmental condition and still perform and produce in spite of thisdisorder.

Donor Parent: The parent of a variety which comprises a genetic locus,gene, or trait of interest which is to be introduced into a secondvariety.

Emasculate: The removal of plant male sex organs or the inactivation ofthe organs with a cytoplasmic or nuclear genetic factor conferring malesterility or a chemical agent.

Essentially all of the morphological and physiological characteristics:A plant having essentially all of the morphological and physiologicalcharacteristics of a designated plant has all of the characteristics ofthe plant that are otherwise present when compared in the sameenvironment, other than an occasional variant trait that might ariseduring backcrossing or direct introduction of a transgene.

Extra Long Staple (ELS): The group classification for cotton in thelongest staple length category. As used in practice and for commerce,ELS denotes varieties belonging to the species G. barbadense that havesuperior fiber qualities, including classification in the longest staplelength category.

F₁ Hybrid: The first generation progeny of the cross of two nonisogenicplants.

Fallout (Fo): As used herein, the term “fallout” refers to the rating ofhow much cotton has fallen on the ground at harvest.

2.5% Fiber Span Length: Refers to the longest 2.5% of a bundle of fibersexpressed in inches as measured by a digital fibergraph.

Fiber Characteristics: Refers to fiber qualities such as strength, fiberlength, micronaire, fiber elongation, uniformity of fiber and amount offiber.

Fiber Elongation: Sometimes referred to as “E1,” refers to theelongation of the fiber at the point of breakage in the strengthdetermination as measured by High Volume Instrumentation (HVI).

Fiber Span Length: The distance spanned by a specific percentage offibers in a test specimen, where the initial starting point of thescanning in the test is considered 100 percent as measured by a digitalfibergraph.

Fiber Strength: Also referred to as “T1,” denotes the force required tobreak a bundle of fibers. Fiber strength is measured in millinewtons(mn) per tex on a stelometer.

Fruiting Nodes: The number of nodes on the main stem from which arisebranches that bear fruit or boll in the first position.

Genotype: The genetic constitution of a cell or organism.

Gin Turnout: Refers to fraction of lint in a machine harvested sample ofseed cotton (lint, seed, and trash).

Haploid: A cell or organism having one set of the two sets ofchromosomes in a diploid.

Linkage: A phenomenon wherein alleles on the same chromosome tend tosegregate together more often than expected by chance if theirtransmission was independent.

Lint Index: The weight of lint per seed in milligrams.

Lint Percent: Refers to the lint (fiber) fraction of seed cotton (lintand seed).

Lint Yield: Refers to the measure of the quantity of fiber produced on agiven unit of land. Presented herein in pounds of lint per acre.

Lint/boll: As used herein, the term “lint/boll” is the weight of lintper boll.

Maturity Rating: A visual rating near harvest on the amount of openbolls on the plant. The rating range is from 1 to 5, 1 being early and 5being late.

Micronaire: A measure of the fineness of the fiber. Within a cottoncultivar, micronaire is also a measure of maturity. Micronairedifferences are governed by changes in perimeter or in cell wallthickness, or by changes in both. Within a variety, cotton perimeter isfairly consistent and maturity will cause a change in micronaire.Consequently, micronaire has a high correlation with maturity within avariety of cotton. Maturity is the degree of development of cell wallthickness. Micronaire may not have a good correlation with maturitybetween varieties of cotton having different fiber perimeter. Micronairevalues range from about “2.0” to “6.0.”

Phenotype: The detectable characteristics of a cell or organism, whichcharacteristics are the manifestation of gene expression.

Plant Height: The average height in meters of a group of plants.

Quantitative Trait Loci (QTL): Genetic loci that control to some degreenumerically representable traits that are usually continuouslydistributed.

Recurrent Parent: The repeating parent (variety) in a backcross breedingprogram. The recurrent parent is the variety into which a genetic locus,gene, or trait is to be introduced.

Regeneration: The development of a plant from tissue culture.

Seed/boll: Refers to the number of seeds per boll.

Seedcotton/boll: Refers to the weight of seedcotton per boll.

Seedweight: Refers to the weight of 100 seeds and is measured in grams.

Self-pollination: The transfer of pollen from the anther to the stigmaof the same plant or a plant of the same genotype.

Single Locus Converted (Conversion) Plant: Plants which are developed bya plant breeding technique called backcrossing wherein essentially allof the morphological and physiological characteristics of a variety arerecovered in addition to the characteristics conferred by the singlelocus transferred into the variety via the backcrossing technique. Asingle locus may comprise one gene, or in the case of transgenic plants,one or more transgenes integrated into the host genome at a single site(locus).

Stringout Rating: also sometimes referred to as “Storm Resistance”refers to a visual rating prior to harvest of the relative looseness ofthe seed cotton held in the boll structure on the plant. The ratingvalues are from “1” to “5” (tight to loose in the boll).

Substantially Equivalent: A characteristic that, when compared, does notshow a statistically significant difference (e.g., p=0.05) from themean.

Tissue Culture: A composition comprising isolated cells of the same or adifferent type or a collection of such cells organized into parts of aplant.

Transgene: A genetic locus comprising a sequence which has beenintroduced into the genome of a cotton plant by genetic techniques, forexample, genetic transformation.

Uniformity Ratio: A measure of the relative fiber span length uniformityof a bundle of fibers. The uniformity ratio is determined by dividingthe 50% fiber span length by the 2.5% fiber span length.

Vegetative Nodes: The number of nodes from the cotyledonary node to thefirst fruiting branch on the main stem of the plant.

DEPOSIT INFORMATION

A deposit of the cotton variety 18R421B3XF, which is disclosed hereinabove and referenced in the claims, was made with the Provasoli-GuillarNational Center for Marine Algae and Microbiota (NCMA) at BigelowLaboratory for Ocean Sciences, 60 Bigelow Drive, East Boothbay, Me.04544 USA. The date of deposit is Oct. 19, 2020, and the accessionnumber for those deposited seeds of cotton variety 18R421B3XF is BigelowNo. 202010027. All restrictions upon the deposit have been removed, andthe deposit is intended to meet all of the requirements of the BudapestTreaty and 37 C.F.R. § 1.801-1.809. The deposit will be maintained inthe depository for a period of 30 years, or 5 years after the lastrequest, or for the effective life of the patent, whichever is longer,and will be replaced if necessary during that period.

The references cited herein, to the extent that they provide exemplaryprocedural or other details supplementary to those set forth herein, arespecifically incorporated herein by reference.

What is claimed is:
 1. A plant of cotton variety 18R421B3XF, whereinrepresentative seed of said variety have been deposited under BigelowAccession No.
 202010027. 2. A plant part of the plant of claim 1,wherein the plant part comprises at least one cell of the plant.
 3. Aseed that produces the plant of claim
 1. 4. A method of producing cottonseed, wherein the method comprises crossing the plant of claim 1 withitself or a second, distinct cotton plant to produce the cotton seed. 5.The method of claim 4, wherein the method comprises crossing the plantof claim 1 with the second, distinct cotton plant to produce F1 hybridcotton seed.
 6. An F1 hybrid cotton seed produced by the method of claim5.
 7. A cotton plant produced by growing the F1 hybrid cotton seed ofclaim
 6. 8. The method of claim 5, wherein the method further comprises:(a) crossing a plant grown from the F1 hybrid cotton seed with itself ora different cotton plant to produce seed of a subsequent generation; (b)growing a progeny plant of the subsequent generation from said seed andcrossing the progeny plant with itself or a second plant to produce seedof a further subsequent generation; and (c) repeating step (b) withsufficient inbreeding to produce seed of an inbred cotton plant derivedfrom cotton variety 18R421B3XF.
 9. The method of claim 8, furthercomprising crossing a plant grown from said seed of an inbred cottonplant derived from cotton variety 18R421B3XF with a plant of a differentgenotype to produce seed of a hybrid cotton plant derived from cottonvariety 18R421B3XF.
 10. A composition comprising the seed of claim 3,wherein the seed is comprised in plant seed growth media.
 11. Thecomposition of claim 10, wherein the plant seed growth media is soil ora synthetic cultivation media.
 12. A seed of cotton variety 18R421B3XFfurther comprising a single locus conversion, wherein representativeseed of cotton variety 18R421B3XF have been deposited under BigelowAccession No.
 202010027. 13. The seed of claim 12, wherein the singlelocus comprises a nucleic acid sequence that enables site-specificgenetic recombination or confers a trait selected from the groupconsisting of male sterility, herbicide tolerance, insect or pestresistance, disease resistance, modified fatty acid metabolism, abioticstress resistance, modified carbohydrate metabolism, and modified cottonfiber characteristics.
 14. A plant grown from the seed of claim
 12. 15.A seed of cotton variety 18R421B3XF further comprising a transgene,wherein representative seed of cotton variety 18R421B3XF have beendeposited under Bigelow Accession No.
 202010027. 16. The seed of claim15, wherein the transgene comprises a nucleic acid sequence that enablessite-specific genetic recombination or confers a trait selected from thegroup consisting of male sterility, herbicide tolerance, insect or pestresistance, disease resistance, modified fatty acid metabolism, abioticstress resistance, modified carbohydrate metabolism, and modified cottonfiber characteristics.
 17. A plant grown from the seed of claim
 15. 18.A method of modifying a cotton plant, wherein the method comprisesintroducing a transgene or a single locus conversion into the plant ofclaim
 1. 19. A method of producing a commodity plant product, whereinthe method comprises collecting the commodity plant product from theplant of claim
 1. 20. A commodity plant product that is produced by themethod of claim 19, wherein the commodity plant product comprises atleast one cell of cotton variety 18R421B3XF.